fishermen not off hook yet
Dioxin role unclear in all Great Lakes
By Susanne Quick
Milwaukee Journal Sentinel
While researchers and fisheries managers across the Great
Lakes region have mostly lauded the study as well-executed,
thorough and comprehensive, they believe the situation is
murky outside the confines of the small, most easterly lake
in the chain.
And they're reluctant to let commercial fishermen and
the exotic sea lamprey off the hook quite yet.
A recent study by a team of researchers from federal
agencies and North American universities demonstrated
that lake trout probably weren't done in by the double-edged
sword of lamprey and commercial fishing in Lake Ontario
- the conventional scenario of this once plentiful fish's
Instead, they say, populations of this top predator were
whittled away as toxic byproducts from combustion and
industrial activities, called dioxins, seeped into the
waters and soils of Lake Ontario - effectively preventing
fertilized eggs from hatching.
"I have to say I was really jazzed when I saw this"
study, said Mike Staggs, director of fisheries at the
Wisconsin Department of Natural Resources. "It provides
a piece" of the lake trout puzzle in the Great Lakes.
But he and other fishery managers across the region remain
circumspect about its meaning elsewhere.
Complicating the situation, it appears that nobody has
data on the dioxin levels in the sediments of lakes other
than Lake Ontario - except for Philip Cook, the primary
researcher of the Lake Ontario study and a research chemist
at the U.S. Environmental Protection Agency.
He has samples of eggs, tissue and sediment from Lake
Michigan in his freezer but has not published his results,
and therefore was reluctant to release the numbers.
Queries to state agencies revealed that samples of these
sorts for the most part have not been collected. And if
they have been, they are incomplete.
So, the question of whether dioxins played a role in
the history of lake trout relies on circumstantial and
correlative data based on historical records of lake trout
numbers, commercial catches and lamprey estimates.
And using this data, everybody - fish biologists and
toxicologists - agrees that at least one lake was immune
to any chemical effect.
The lake trout population in Lake Superior, which holds
nearly 3,000 cubic miles of water and has relatively few
potential dioxin producers on its shores, was unlikely
to have succumbed to the chemical culprit. Here, the lake
trout die-off was most likely the result of excessive
commercial fishing and lamprey.
Indeed, subsequent lake trout management on Lake Superior
supports this observation. The closing of commercial fishing
in 1961 and programs designed to actively reduce lamprey
populations brought back lake trout numbers to near historical
highs, concluded Mike Hansen, a fisheries biologist and
professor of fisheries at the University of Wisconsin-Stevens
Point, in a paper in the Journal of Great Lakes Research
However, the same can't be said for Lake Michigan, where
similar measures have been taken to bring back lake trout.
And this is where the dioxin puzzle-piece may fit in,
said Staggs. Although, he acknowledges that debate resounds
on this score, too.
For instance, while Hansen agrees that "Lake Michigan
would seem to be the most likely lake where similar levels
of contamination" to Lake Ontario may have been present,
he cited a 2002 study from another group of federal and
university researchers, who "found no basis for invoking
contamination in the demise of lake trout or the continued
failure of lake trout to reproduce."
"Most people want to believe that contaminants cause(d)
problems with fish reproduction, so any evidence that
suggests such a linkage is quite appealing," he said
in an e-mail, qualifying his statement by saying that
he had not read the Lake Ontario paper thoroughly, nor
is he a lower Great Lakes specialist.
But, he "can find no one in the fishery community
who actually believes that contaminants were implicated
in the demise of any fish population in the Great Lakes,
though some contaminant experts continue to beat the drum."
Levels in water are low
Mike Hammers, a wastewater engineer with the DNR, is dubious,
Wisconsin paper mills release minute amounts of dioxin
into Wisconsin lakes and rivers, he said, but they fall
far below the numbers cited in the Lake Ontario study.
"We're talking 3 parts per quintillion," -
a millionth the amount of the Lake Ontario numbers, he
"I can't tell you what was there in the past,"
Hammers said, but the levels now found in the water column
- near areas where discharge from paper mills and factories
enters the environment - are much smaller than the amounts
thought to cause problems.
But to Cook, the lead researcher on the Lake Ontario
study, comparing water column numbers with sediment and
egg analyses is like comparing apples and watermelons.
And although formulas have been devised to compare the
two, the real test is to look at the content in the eggs
- a task he is working on.
The bottom line, he said, is that no one knows the minimum
levels of dioxin that affect lake trout. So although low
levels might not necessarily kill developing eggs - as
was seen in the Lake Ontario study - there might be other
harmful side effects.
These low-level effects, called sub-lethal effects, are
believed to cause problems ranging from neurological and
cardiac deficiencies to blindness. And the effects on
the reproduction - and viability - of adult fish remains
a question, Cook said.
"Their vulnerability may be greater than what we
have documented," he said. "We just don't know
at this point."
Studies on rainbow trout, using chemical cocktails that
mimic the levels, profiles and configurations of Lake
Michigan dioxins, have shown sub-lethal effects such as
delayed hatch timing, mild hemorrhaging and swelling of
the yolk sac, said Richard Peterson, a toxicologist at
UW-Madison, and one of the authors on the Lake Ontario
But "we still have a big information gap" on
sub-lethal effects, he said.
Yet, both he and Cook are concerned because lake trout
appear to be more sensitive to dioxins than other fish.
Why this is so is not known, said Peterson. "That's
the million-dollar question."
Maybe, said Roger Bergstedt, a research fishery biologist
with the U.S. Geological Survey who was not involved in
the study. But as far as he is concerned, the search for
what happened to lake trout is irrelevant.
"Current management requires that we try to keep
lamprey populations down," he said. If we let them
be, they'll come back in force.
He cited work he had done on Lake Erie, where a four-
or five-year hiatus in treating streams for lamprey created
a boom in the blood-sucking critters.
"Mortality rates of lake trout became unacceptable,"
The point now, he said, is to manage what we have.